"... there is a stone in name called Iris: digged out of the ground it is in a certaine Island of the red sea, distant from the city Berenice three score miles. For the most part it resembleth Crystall: which is the reason that some hath tearmed it the root of Crystall. But the cause why they call it Iris, is, That if the beames of the Sunne strike upon it directly within house, it doth send from it against the walls that bee neare, the very resemblance both in forme and also in colour of a rainebow; and eftsoones it will chaunge the same in much varietie, to the great admiration of them that behold it. For certain it is knowne, that six angles it hath in manner of the Crystall: but they say that some of them have their sides rugged, and the same {40} unequally angled: which if they be laid abroad against the Sunne in the open aire, do scatter the beames of the Sunne, which light upon them too and fro: also that others doe yeeld a brightnes from themselves, and thereby illuminat all that is about them. As for the diverse colours which they cast forth, it never happeneth but in a darke or shaddowie place: whereby a man may know, that the varietie of colours is not in the stone Iris, but commeth by the reverberation of the wals. But the best Iris is that which representeth the greatest circles upon the wall, and those which bee likest unto rainebowes indeed." In the English translation of Solinus's _De Mirabilibus_ (_The excellent and pleasant worke of Julius Solinus containing the noble actions of humaine creatures, the secretes and providence of nature, the descriptions of countries ... tr. by A. Golding, gent._, Lond., 1587), chapter xv. on Arabia has the following: "Hee findeth likewise the Iris in the Red sea, sixe cornered as the Crystall: which beeing touched with the Sunnebeames, casteth out of him a bryght reflexion of the ayre like the Raynebowe." Iris is also mentioned by Albertus Magnus (_De mineralibus_, Venet., 1542, p. 189), by Marbodeus Gallus (_De lapidibus_, Par. 1531, p. 78), who describes it as "crystallo simulem sexangulam," by Lomatius (_Artes of curious Paintinge_, Haydocke's translation, Lond., 1598, p. 157), who says, "... the Sunne, which casting his beames vpon the _stone Iris_, causeth the _raine-bowe_ to appeare therein ...," and by "Sir" John Hill (_A General Natural History_, Lond., 1748, p. 179). Figures of the Iris given by Aldrovandi in the _Musæum Metallicum_ clearly depict crystals of quartz.